Compressor unloading device



June 22, 1937. B. s. AIKMAN 2,084,665

CQMPRESSOR -UNLOADING DEVICE Fi'ied May 15, 1936 22 L62 6| 54 F 23 56 6 --5a INVENTOR BURTEIN S. AIKMAN ATTORNEY v Patented June 22, 1937 UNITED STATES PATENT OFFICE COMPRESSOR UNLOADING DEVICE Burton S. Aikman, Wilkins burg, Pa., assignor to The Westinghouse Air Brake Company, Wilmerding, Pa., a corporation of Pennsylvania Application May 15, 1936, Serial No. 79,938 1 Claim. (01. 230-27) vide a novel arrangement whereby a compressor 1 unloader device is controlled automatically according to the speed of the compressor. More 1 specifically, the novel arrangement provides for control ofthe unloader device according-to the degree of partial vacuum produced in the crank case of a compressor by operation of the compressor.

The above and other objects oi. my invention which will be made apparent subsequently are attained by an illustrative embodiment of the invention hereinafter described and shown in the accompanying drawing wherein the single flgure is a fragmentary view, mostly in section,

showing my unloader device and its arrangement with a compressor. 35 Referring to the drawing, the compressor shown comprises an upper casing section forming a. compression cylinder i, and a lower casing section forming a piston guide cylinder 2 and a crank case chamber 3. Projecting from the guide cylinder 2 is an annular flange 4 of L cross section, the end flange 5 on the compression cylinder i cooperating with the upper edge of the flange 4 and being suitably secured thereto as by bolts, not shown. The flange 4 forms an annular space 86 or chamber 1 which is open to atmosphere through one or more ports 5 in the flange.

The bore 8 of the compression cylinder i is larger than the bore ii in the guide cylinder -2 and opens at its lower end into the ,chamber 1, hereafter called the intake chamber.

A piston I3 is provided having a pressure head I4 slidable in the bore 9 and a guide flange or skirt II, of smaller diameter than the head i4, slidable in the'bore ii. Thepiston I3 may be recipro- 45 cated in the well known mannerby rotation of a crank shait H, the crank shaft having an eccentric I! connected by a connecting rod I8 to a wristpin 2| onthepiston. v 60 Any suitable type of intake valve may be provided for admitting air into; the compression chamber 22 as for example, a ring valve 23 mounted on the piston head 14 for controlling a series of intake ports 24 which extend through the outer ss periphery of the pressure head of the piston. On

' conduit, or passage 53.

the up or compression stroke of the piston, the ring valve 23 moves into seated position to close the ports 24 and, on the down or intake stroke of the piston, unseats to admit air from the intake chamber 1 to the compression chamber 22 through the ports 24. a H

4 Any suitable type or dischargevalve may be provided, as for example, a springloaded disc valve 21 for closing the discharge port 28, opening out of the compression chamber 22, on the 10 intake or down stroke of the piston, and for permitting the flow of fluid compressed in the compression chamber 22 out through the discharge port to a discharge pipe 22, on the compression or up stroke of the piston. 15

According to my'invention, I provide an unloader valve device 12 interposed in the discharge pipe 29 between the compressor and a suitable reservoir 3!. 1

The unloader valve device 32 comprises a casing 34 which may be mounted conveniently as a separate unit, in any desired location or which may constitute an integral or attached part of the compressor casing.

Formed in the casing 34 is a chamber 36 open to the portion of the discharge, pipe 29 leading to the reservoir 33 and containing a spring loaded check valve 31 for preventing back flow from the reservoir "to a passage or chamber 38, to which is connected the portion of the discharge pipe 29 leading from the compressor. The passage 38 opens through a port 39 into a bore in the v casing, which bore is constantly open to atmosphere through a port 42. A pin valve 44 is provided for closing the port 39 and is formed on the end of the stem 46 of an operating piston or movable abutment" which is contained in a bore 48 that is open at the outer end thereofv to atmosphere, the casing having an inwardly extending flange 49 at the outer end of the bore 48 for 4 urges the piston outwardly of the bore 48 to unseat the pin valve 44 and open port 39. The chamber 52 is constantly connected to the crank case chamber 3 of the compressor as by a pipe, 5

Any suitable device for producing a partial vacuum in the crank case chamber .3 by operation of the compressor may be provided, as for example the check valve device '4 in the pres- 55 54 comprises a ball valve 55 adapted to seat on a conical valve seat 56 to close a port 51 through the pressure head of the piston l3, upon the up or compression stroke of the piston. The ball valve 55 is contained in a recess 59 of a. screw plug 6| removably secured to the piston head l4,

1 the recess 59 being open to the compression chamher 22 through a plurality of ports 62. On the down or intake stroke of the piston l3, the ball valve 55 unseats and permits air to pass from the crank case chamber side of the piston into the compression chamber 22. I

It will be understood that upon continued reciprocation of the piston l3, air is continually forced out of the crankcase chamber 3 into the' a restricted passage 65 is provided which connects the crank case chamber 3 to atmosphere, and .which may be suitably located and so designed that until the speed of the compressor, that is the rapidity with which the piston I3 is reciprocated,

exceeds a certain uniform speed, the rate of influx of air through the passage 65 into the crank case chamber 3, may equal the rate at which it is taken out of the crank case chamber by operation of the check valve device 54. Thus until the speed of the compressor exceeds the said certain uniform speed, as on starting, the crank case chamber remains at atmospheric pressure. Thereafter, as the speed of the compressor increases, the rate at which air is discharged from the crank case chamber by operation of the check valve device 54 exceeds the rate at which it is capable of flowing into the crank case chamber through the passage 65 and consequently a partial vacuum is produced in the crank case chamber, the degree of vacuum increasing with the increase inspeed of the compressor above the certain uniform speed.

Conversely, as the speed of the compressor re.- duces below the certain uniform speed, atmospheric pressure is restored in the crank case chamber.

In operation, with the compressor at rest, the pin valve 44 of the unloader device 32 is unseated to open port 39 and thus open the compressor side of pipe 29 and passage 38 of the unloader device to atmosphere through port 42, the check valve 31 being effective to prevent. back flow of air from the reservoir 33 into passage 38 and to atmosphere. It will be understood, that when the crank case'chamber is at atmospheric pressure, as it is when the compressor is stopped, then the annular chamber 52 of the unloader device is also at atmospheric pressure, and thus that spring 5| acts to shift the piston 41 outwardly and thus unseats the pin valve 44. I

As the compressor begins to operate no partial vacuum is created in the crank case chamber until the certain uniform speed is exceeded, this uniform speed depending upon the flow capacity of the restricted passage 65. As the degree of P11 tial vacuum increases after the compressor exceeds the certain uniform speed. a fluid pressure unbalance is created on the piston 41 of the unloader, due to the fact that annular chamber 52 v 2,084,865 sure head I4 of piston l3. The check valve device is at a lower pressure than the atmospheric pressure acting on the outer .face of the piston 41, which lower pressure corresponds to the degree of partial vacuum in the crank case chamber. When a suflicient difierential fluid pressure force is effective on the piston, as for example five to ten pounds, the piston moves upwardly in bore 48 to cause the pin valve 44 to close port 39. Communication between the compressor portion of discharge pipe 29 and atmosphere being thus cut off, the fluid compressed by the compressor and discharged into pipe 29 can only escape past the check valve 31 into the reservoir'33. Thus'loading of the compressor is effected only after the compressor has exceeded a certain predetermined speed.

Obviously, the greater the degree of vacuum produced in the crank case chamber and in annular chamber 52, the greater is the differential fluid pressure force acting on the piston 41 to hold pin valve 44 seated. However, even at the minimum degree of vacuum in crank case chamber 22 which will cause seating of the pin valve 44, the force holding the pin valve seated is sufficient to resist unseating of the pin valve 44 due to maximum fluid pressure acting in passage 38 on the inner seated or end face of the pin valve 44. Observation of the relatively small area of the pin valve 44 and the relatively large area of the piston 41- will render this fact readily apparent. It will be understood that by increasing the area of the piston 41, the piston will be responsively moved to determined speed beyond which it is necessary for the compressor to operate before loading is effected, may be made any selected speed.

When the speed of the compressor decreases, as

"a result of an increase in load thereon or of stopping the compressor, the degree of partial vacuum in the crank case decreases accordingly, and when the speed of the compressor has decreased sufl'lciently so that the differential fluid pressure force acting on the piston 41 is inadequate to hold the pin valve'44- seated against the force of the fluid pressure in passage 38 acting on the end of the pin valve 44, the piston will bemoved outwardly, assisted by the tension of the return spring 5!, to unseat the pin'valve 44 and open to atmosphere that portion of discharge pipe 29 leading from the compressor, the compressor being thereby unloaded.

The spring 5| is, as previously stated, only lightly tensioned and may be omitted'if desired, since the piston 41 will be actuated to seat and pressor when the speed of the compressordecreases below a certain uniform speed and for loading thecompressor when the speed of the compressor increases above the certain uniform speed.

I appreciate that various omissions, additions or modifications may be eflected with respect to u the compressor may be provided for closing the I restricted passage 65 after the unloader device 32 has operated to load the compressor, so that as long as the compressor continues to operate above a certain speed, the passage 85 will be closed and thus enables, relatively high degree- 01' partial vacuum to be produced in the crank case chamber and in chamber 52 of the unloader device 32, to the end that the higher fluid pressure diflerential acting on piston 41 will more positively hold the pin valve 44 seated against leakage therepalst.

It is not my intention, therefore, to limit the scope or my invention except as necessitated by the scope of the prior art.

Having now described my invention, what I' claim as new and desire to secure by Letters Patcut, is:

In combination, an air compressor comprising a compression chamber, a crank case chamber, a

reciprocatlve piston effective to compress air in said compression chamber, a check valve in the pressure head of the piston eflective upon reciprocation ot the piston to cause withdrawal of air from the crank case chamber to the compression chamber and thereby tend to cause a partial vacuum in the crank case chamber, a. restricted passage through which air may flow into the crank case chamber at any rate up to a maximum rate, said check valve being lneflective to produce a partial vacuum in the crank case chamber un- 4 less the speed of operationof the compressor exceeds a certain uniform speed beyond which i 'the rate of withdrawal of air from the crank case chamber by said check valve exceeds the maximum rate of flow of air into the crank case chamber through said restricted passage, the degree of the partial vacuum created in the crank case chamber varying in accordance with the speed of the compressor'above the certain uniform speed, and means eifective to unload the compressor as long as the partial vacuum in the crank case chamber does not exceed a certain predetermined degree and operative when the partial vacuum exceeds 'said certain degree to cause loading of the compressor.

BURTON S. AIKMAN. 

